The present invention relates to processes for the hydrodechlorination of chlorinated hydrocarbons and to the catalysts employed therein, and more specifically relates in this broader aspect to methods of preparing these catalysts.
In the chlorofluorocarbon art, EP 0 459 463 A1 to Daikin Industries, Ltd. describes the preparation of 1-chloro-1,2,2-trifluoroethylene or 1,2,2,-trifluoroethylene, by reacting 1,1,2-trichloro-1,2,2,-trlfluoroethane and hydrogen in the presence of a supported bimetallic catalyst comprising a "basic metal" (Pd, Rh or Ru) and an "additive metal" (Hg, Pb, Cd, Sn, In, Cu, Bi, Tl or Ag). The method shown for making these catalysts involves making a salt solution of an "additive" metal in water, adding to this solution a quantity of formalin (a solution of formaldehyde in water and methanol) and a supported "basic metal" catalyst in pellet or powder form, aging the mixture at 50 degrees Celsius for 2 to 3 hours, then drying the catalyst and pretreating with hydrogen at 300 to 400 degrees Celsius for 2 hours (all of the additive metals besides bismuth) or with oxygen at 300 degrees Celsius for the same 2 hours (where bismuth is the additive metal).
Outside of the chlorofluorocarbon art as such, however, a number of processes are described for converting a chlorinated hydrocarbon to a less-chlorinated hydrocarbon and hydrogen chloride via catalysts made by other methods, exemplary hydrodechlorination processes being those described in EP 015665 (converting 1,1,2-trichloroethane to ethylene or vinyl chloride), GB 1 400 529 (converting "hydrocarbon chlorides" to "chlorine-free hydrocarbons"), DD 235 630 A1 (converting 1,2-dichloropropane to propylene), U.S. Pat. Nos. 4,818,368, 4,882,037 and 4,923,590 (the hydrogenation of halogenated hydrocarbons), CA 1 119 203 (converting perchloroethylene to trichloroethylene), DE 3 804 265 A1 (same) and U.S. Pat. No. 5,091,603 (same).
Commonly-assigned U.S. patent application Ser. No. 08/112,042, now abandoned (which has been published under the Patent Cooperation Treaty as WO 94/07828), and U.S. application Ser. No. 08/227,812, filed as a continuation-in-part of the '042 application and now allowed, U.S. Pat. No. 5,453,557, are of particular relevance or interest, and similarly describe processes for converting a chlorinated alkane, for example 1,2-dichloropropane to a corresponding less-chlorinated (including non-chlorinated) alkene (propylene for 1,2-dichloropropane) and hydrogen chloride. The catalysts described in the '812 application more particularly are preferably bimetallic catalysts of an active hydrogenating metal (inclusive of the preferred Group VIII metals such as platinum (as per the '042 application) and being inclusive also of chromium, tungsten and molybdenum) and of a surface segregating metal (preferably being a Group IB metal of copper, silver or gold, copper being especially preferred) on a support (which is preferably a carbon support). A most preferred catalyst from the '042 and '812 applications, which applications are incorporated herein by reference, is a bimetallic catalyst of platinum and copper on a commercially-available BPLF3 grade carbon from Calgon Carbon Corporation, Pittsburgh, Pa.
Methods described or exemplified for making this Pt/Cu bimetallic catalyst in the '042 and '812 applications essentially involve coimpregnation of the carbon support from a solution of platinum and copper salts (e.g., chloroplatinic acid and CuCl.sub.2), air-drying under ambient conditions, and oven drying at an elevated temperature prior to reduction with hydrogen and/or pretreatment by exposure to a chloride source.